Benzidine rearrangement - Benzidine rearrangement

When aromatic hydrazo compounds are treated with strong acid, various rearrangement products including benzidine are produced. Such rearrangement reactions are collectively called the benzidine rearrangement. In the case of hydrazobenzene, the main products are benzidine (about 70%) and diphenyline (about 30%), but depending on the ring structure and substituents, other types of rearrangement products may predominate. For example, when -COOH, -SO ₃ H, etc. are present at the para position, these groups are eliminated to form benzidine compounds, but halogens, -OAc, -OR, -NRAc, -NR ₂ , -R, etc. are difficult to eliminate, resulting in diphenyline, semidine, etc. The benzidine rearrangement is an intramolecular rearrangement reaction that is thought to proceed through an intermediate in which both amino groups are protonated, as shown below, followed by cleavage of the N-N bond to reach the product.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

芳香族ヒドラゾ化合物を強酸で処理すると，ベンジジンをはじめ種々の転位生成物を生じる．このような転位反応を総称してベンジジン転位という．ヒドラゾベンゼンの場合の主生成物は，ベンジジン(約70％)とジフェニリン(約30％)であるが，環の構造や置換基によって，ほかの型の転位生成物が主となる場合もある．たとえば，パラ位に-COOH，-SO₃Hなどがある場合は，これらの基が脱離してベンジジン化合物になるが，ハロゲン，-OAc，-OR，-NRAc，-NR₂，-Rなどは脱離しにくく，ジフェニリン，セミジンなどが生じる．ベンジジン転位は分子内転位反応で，次のように二つのアミノ基がともにプロトン付加された中間体を経てN-N結合が切断し，生成物に至るものと考えられている．

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